Production of familial, non-modular, plural color patterns on a moving substrate

ABSTRACT

A method of continuously producing a continuous paint coat of substantially constant, pre-determined thickness, and displaying a plural colour, familial, non-modular pattern, on a surface of a moving substrate, comprising the steps of depositing at least two discontinuous, randomly patchy, differently coloured, component paint deposits, at a predetermined, constant, long term deposition rate for each component deposit in terms of the volume of paint per unit area of the surface, within a single stationary target area of the surface, or within stationary target areas of the surface respectively associated with the component deposits and at least partly aligned in the direction of movement of the substrate, and thereafter spreading and smoothing the component paint deposits carried by the substrate from the target area or areas, to form the continuous coat.

TECHNICAL FIELD

This invention relates to the continuous application of liquid orsemi-liquid paint coatings to a moving substrate.

The invention was devised primarily for the application of coatings ofpaint to metal strip, for example steel strip coated with a corrosionresistant metallic alloy, and is described primarily in that contexthereinafter. However it will be apparent that it is applicable to theapplication of paint coatings to substrates of other materials, providedthe substrate is substantially impervious to the coating and, at leastin preferred embodiments of the invention, is capable of being heated toabove the glass transition temperature of a solid paint composition tobe applied to the substrate.

BACKGROUND ART

The application of paint to steel strip in large scale, continuouslyoperating, steel finishing mills is a highly developed art.

Typically, the substrate strip is progressed through a coating stationwherein liquid paint, comprising pigments and other paint solidsdissolved in a solvent or otherwise dispersed in a liquid carrier, isapplied to the substrate by a dipping, spraying, roller coating or likeprocess for applying a liquid film to the substrate, which film issubsequently allowed or caused to evaporate to leave a solid paint coaton the substrate.

It is also known to apply paint composition to a heated substratewherein the paint is applied as a liquid melted from a solid body ofsubstantially solvent free paint composition by contact of the bodywith, or near approach of the body to, the hot substrate. In thiscontext the term “liquid” includes high viscosity liquids, that mayapproach soft, plastic solids in nature, as well as easily flowingliquids.

That last mentioned mode of depositing liquid material on a substrate isreferred to as “melt deposition” and the deposited liquid is referred toas a “melt deposit” hereinafter.

Previously the deposition rate of melt deposits was determined bycontrolling the contact pressure between the solid paint body and thesubstrate, while maintaining constant all of the many other parametersaffecting the deposition rate. Such a process is described in U.S. Pat.No. 3,630,802 to Dettling.

The difficulty of accurately controlling all of those parameters makesit difficult to obtain constant deposition rates of low value when usingDettling type pressure controlled melt deposition processes. This leadto their replacement, in painting operations, by the melt depositiontechnique described in our Australian patent No. 667716.

Briefly stated, that Australian patent discloses depositing a polymerbased coating composition onto a side of a substrate metal strip movingat a constant speed, by heating the strip to a temperature above theglass transition temperature of the composition, and driving a solidblock of the composition towards the strip at a predetermined blockspeed.

It is then only necessary to control the block speed to cause a meltdeposit to be applied to the strip at a precisely controlled depositionrate, without the need to closely control other operating parameters, inthat each of those other parameters need only lie within a broad rangeof working values.

As is also disclosed in that Australian patent, the melt deposit maythen be spread over the surface of the strip by a pressure roll toemerge as a smooth, wet coating on the strip.

Irrespective of the mode of deposition, the prior art has beenrestricted to the production of mono-chrome product, wherein a uniformcoating is applied to the whole of at least one side of the substratestrip.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide ornamental, pluralcolour paint coatings, wherein the differently coloured components ofthe coating are applied during a single pass of a substrate through apainting station.

It is well known that some patterns displaying random variation, in thesense that no repeating module of the pattern may be discerned, may,nevertheless, be seen as being members of a family of related patterns,in the sense that individual expressions of the randomly variablepatterns of one family have a recognisable family similarity, enablingthem to be readily distinguished, by eye, from individual expressions ofthe randomly variable patterns of other families.

Wood grain patterns may be cited as typical examples of patterns of thekind referred to in the preceding paragraph. One has no difficulty indistinguishing between veneers of, for example the four “families” ofleak, pine, mahogany, and silky oak, although no two pieces of veneer ofany one timber are identical.

Such randomly variable patterns maintaining a family resemblance arereferred to as “familial, non-modular patterns” hereinafter.

The concept of familial, non-modular patterns is of significance to thepresent invention. If, for example, a domestic appliance has a cabinetmade of panels of plural coloured, painted sheet steel, it is desirablethat there be no discernible repetition of the pattern in any one panelor from panel to panel of the appliance, but it is also desirable thateach panel bears a strong family resemblance to the others.

Thus, another object of the present invention is to provide for thecontinuous application of a paint coat displaying a familial,non-modular, colour pattern to a substrate, during a single pass of thesubstrate through a painting station.

Still another object is to provide for the reproducibility of the familylikeness of familial coatings produced by painting operations that maybe spaced apart in time.

Meeting that last objective enables a steel finisher, for example, toaccept orders for painted strip identified by reference to a familial,non-modular coating illustrated in a catalogue, in the knowledge that hemay produce new product that may never display an exact reproduction ofthe catalogue illustration, but which will nevertheless be regarded bythe purchaser as an acceptable expression of the catalogue illustration.

The present invention is based on the experimentally determineddiscovery that if two or more differently coloured paints are applied asdiscontinuous, randomly patchy deposits to a stationary target area of amoving substrate, or respectively to stationary target areas that arealigned in the direction of travel of a substrate, then, provided thelong term deposition rates, in terms of the volume of the deposit perunit area of the substrate surface that is to be painted, isappropriately chosen and closely controlled, those deposits may bespread and smoothed to form a continuous coat of desired thicknesscovering a larger area of the substrate surface and displaying afamilial, non-modular striated pattern. Surprisingly, even if the paintsare similar in composition and are readily miscible, it has been foundthat the respective colours remain visible as distinct colours in thecontinuous coat.

Furthermore, the experiments leading to the present invention have shownthat if the individual long term deposition rates of the componentdeposits and the positioning of the target area or areas for eachcomponent deposit are reproduced from one operation to another, then thenon-modular pattern resulting from each operation will display anunchanging family resemblance. On the other hand, if any one or more ofthose deposition parameters is changed, the resultant continuous coatwill be discerned as belonging to another family.

As of now, the particular family characteristics of any selection ofthose parameters cannot be readily forecast in advance, and it isnecessary to trial any particular selection to determine whether it willproduce a pleasing result. However experiments have conclusivelydemonstrated that the family character of any selection will bereproduced by the same selection on each different occasion.

Therefore, the invention consists in a method of continuously producinga continuous paint coat of substantially constant, pre-determinedthickness, and displaying a plural colour, familial, non-modularpattern, on a surface of a moving substrate, comprising the steps ofdepositing at least two discontinuous, randomly patchy, differentlycoloured, component paint deposits, at a predetermined, constant, longterm deposition rate for each component deposit in terms of the volumeof paint per unit area of the surface, within a single stationary targetarea of the surface, or within stationary target areas of the surfacerespectively associated with the component deposits and at least partlyaligned in the direction of movement of the substrate, and thereafterspreading and smoothing the component paint deposits carried by thesubstrate from the target area or areas, to form the continuous coat.

As the component deposits are discontinuous and patchy theirinstantaneous deposition rates are constantly varying, thus the term“long term deposition rate” is used herein to indicate the average ratewhen taken over an area of the substrate surface large enough to ensurethat an equivalent steady state figure is determined. Typically, thetotal volume of a component deposited on say, 0.5 to 1.0 square metersof the substrate surface may be regarded as the component's “long term”deposition rate.

The invention is not limited to a particular mode of deposition of thecomponent deposits provided they meet the above criteria, however inpreferred embodiments of the present invention a melt depositionprocess, using constant substrate speed and controlled block speed, ofthe kind described above, is used in respect of each component deposit.

It has been found that if the block speed is low enough, the meltdeposit is in the form of relatively thick, randomly positioned gobbetsof paint. Thus melt deposition using block speed control is ideal forthe purposes of the present invention, in that notwithstanding therandomly patchy nature of the melt deposit, the long term depositionrate on a constant speed substrate is still accurately determined by theblock speed.

Also, the target area for a deposit, being the area of the block tosubstrate interface, is accurately defined, and fully blanketed in thelong term by the deposited material. Thus, if the strip speed isconstant, melt deposition using block speed control may provide all theabove described characteristics of a component deposit as that term isused herein, namely a randomly patchy deposit applied to a movingsubstrate at an accurate long term rate, in terms of volume of paintdeposited per unit area of the substrate surface, applied within apredetermined stationary target area of the substrate surface.

Therefore according to a first preferred embodiment, the inventionprovides a method of painting at least a part of a side face of a movingsubstrate strip utilising a paint composition having a glass transitiontemperature, of the kind comprising the steps of pre-heating the stripto a pre-heat temperature above said glass transition temperature,moving the pre-heated strip at a pre-determined strip speed, driving asolid block of the paint composition along an axis of the block at apre-determined block speed towards said side face to cause a liquiddeposit of said paint composition to be melted from the block andcarried away from the block on said face, spreading and smoothing thecarried away liquid deposit, and thereafter allowing or causing thesmoothed liquid deposit to solidify, characterised in that said blockcomprises at least two differently coloured components, in that thepre-heat temperature is above the glass transition temperatures of allof the components, in that the block speed is so low as to ensure thatthe carried away deposit is a discontinuous patchy deposit, and in thatthe spreading and smoothing converts the discontinuous patchy depositinto a continuous coat displaying a familial, non-modular colourpattern.

According to a second preferred embodiment the invention provides amethod of painting at least a part of a side face of a moving substratestrip utilising a paint composition having a glass transitiontemperature, of the kind comprising the steps of pre-heating the stripto a pre-heat temperature above said glass transition temperature,moving the pre-heated strip at a predetermined strip speed, driving asolid block of the paint composition along an axis of the block at apre-determined block speed towards said side face to cause a liquiddeposit of said paint composition to be melted from the block andcarried away from the block on said face, spreading and smoothing thecarried away liquid deposit, and thereafter allowing or causing thesmoothed liquid deposit to solidify, characterised in that at least onefurther said block at least partly differing in colour from the firstmentioned block and in at least partial alignment with the firstmentioned block in the direction of strip travel is likewise driventowards the side face at a second pre-determined block speed, which mayor may not differ from the first mentioned block speed, in that eachblock speed is so low as to ensure that each of the carried awaydeposits is a discontinuous patchy deposit, and in that the spreadingand smoothing converts all of the carried away deposits into acontinuous coat displaying a familial, non-modular colour pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example, several embodiments of the above described inventionare described in more detail hereinafter with reference to theaccompanying drawings.

FIG. 1 is a diagrammatic front elevation of a painting station suitablefor effecting methods according to the said first preferred embodimentof the invention.

FIG. 2 is a diagrammatic sectional elevation taken on line A—A of FIG.1.

FIG. 3 is a view similar to FIG. 1 of a painting station suitable foreffecting methods according to said second preferred embodiment of theinvention.

FIG. 4 is a diagrammatic sectional elevation taken on line A—A of FIG.3.

FIG. 5 is a perspective view of a two component paint block useable inmethods according to said first or second preferred embodiments of theinvention.

FIGS. 6(a), 6(b), 6(c), 6(d), and 6(e) are diagrammatic front elevationsof sets of three, two component paint blocks useable in methodsaccording to said first or second preferred embodiments of theinvention.

FIGS. 7, 8, 9 ,10, 11, 12, and 13 respectively are black and whitedepictions of familial, non-modular patterns on painted steel stripproduced by exemplary embodiments of the invention.

BEST MODE OF CARRYING OUT THE INVENTION

The apparatus illustrated by FIG. 1 and 2, except for the nature ofpaint blocks 23 therein, is an essentially conventional melt depositionstation, and need not be described in detail herein. It may be includedas a component of a continuous paint line in a steel strip finishingmill. It comprises a steel back-up roll 21, a spreading and smoothingroll 22 with an elastomeric outer cylindrical surface layer and threepaint blocks 23. Each paint block 23 comprises two or more componentpaint compositions of differing colours, as is described more fullybelow.

A steel strip 24 which is to be painted moves vertically upwardlytowards the roll 21, turns through approximately 90 degrees as it passesover that roll and leaves the station more or less horizontally, havingbeen passed through the nip of rolls 21 and 22. Both rolls are powerdriven and their surface speeds are not necessarily the same. Theback-up roll 21 is preferably driven so that its surface speed issubstantially the same as that of the strip 24, and that part of theroll touching the strip moves in the same direction as the strip. On theother hand the surface speed of the spreading and smoothing roll 22 mayrange between a slow speed in the opposite direction to the movement ofthe strip, through zero up to about 25% of the speed of the strip in thesame direction as the movement of the strip. The speed of the strip 24is kept constant and the paint blocks 23 are driven towards the strip byany appropriate speed controllable block feed device, for example, anendless belt conveyor carrying the blocks.

Before reaching the melt deposition station, the strip 24 is cleaned andotherwise readied to receive a paint coat. It is pre-heated to atemperature in excess of the glass transition temperatures of thecomponent compositions of the blocks 23. Thus, paint composition ismelted from the blocks 23 and deposited on the strip at a long termdeposition rate determined by the block speed, and is carried by thestrip to and through the nip of the two rolls 21 and 22.

In accordance with the invention, the block speed is so low as to ensurethat the carried away melt deposit is a discontinuous patchy deposit,and a pressure is maintained between the rolls 21 and 22 that issufficient to spread that melt deposit into a smooth, continuous coat ofdesired thickness preferably covering the side of the strip.

Also in accordance with the invention, each of the blocks 23 comprisesat least two, unblended differently coloured components, and this,surprisingly, results in the continuous coat displaying a familial,non-modular pattern, in which, it has been found, the family resemblanceis uniquely determined, in each instance, by the relative proportionsand dispositions of the components in the blocks.

For example, if each of the blocks 23 is a marbled block, such asillustrated by FIG. 5, wherein there is 17 parts by weight of the darkercomponent to 13 parts by weight of the lighter component, a patternexemplified by the sample length thereof shown by FIG. 7 is produced.The block of FIG. 5 is randomly marbled, it may be produced by placingappropriate quantities of large fragments of the solid components in amould, and warming the mould and its contents sufficiently to cause thecomponents to coalesce without mixing. The volume proportions of thecomponents of the block may be selected as needed to produce differentcontinuous coating patterns.

In other examples, a non-random arrangement of the block components maybe obtained, for example by simultaneous extrusion of the warmcomponents through a multi-orifice die, or multi nozzle extruder.Several such blocks, each of two components, are shown in FIGS. 6(a) to6(e) respectively.

It will be apparent that each of the multi component blocks illustratedby FIGS. 6(a) to 6(e) may be made as a unit, but alternatively therespective single coloured components may be laid up, one upon or besidethe other, on a block feed conveyor to obtain the same effect. In thisregard it should be borne in mind that the blocks are naturally adhesiveto an extent enabling the laid up components to function as a single,plural coloured block.

It should be emphasised that the illustrated blocks are merely exemplaryand there is an almost unlimited variety of similar blocks of two ormore components, that could be used. All of the illustrated blocks,except for that of FIG. 6(c), show substantially equal volumes of eachcomponent in the finished block, but the actual proportions that may beused in any instance are purely a matter of choice, and determine thenature of the familial, non-modular pattern ultimately produced.

Again by way of example, reference is made to FIGS. 8 and 9, whichdemonstrate the dependency of the family resemblance of the finishedpattern on the arrangement of the block components. FIG. 8 shows asample pattern obtained when the blocks 23 conform with blocks 6(a) andwhen the lighter coloured layers of the blocks are the lower layers asthe blocks are presented to the upwardly moving strip, whereas FIG. 9shows the pattern produced by the same blocks when the lighter colouredlayers are the upper layers. Somewhat surprisingly, the layer that isfirst met by the strip is dominant in the finished pattern, whereas onewould intuit that the second met layer would dominate, as at times itwould presumably be deposited on top of a patch of the first met layer.

FIGS. 3 and 4 show apparatus suitable for said second preferredembodiments of the invention. It differs from the FIGS. 1 and 2apparatus only in that two independently controllable block feed devicesare provided, for two sets of blocks 23(a) and 23(b) instead of thesingle feed device of the earlier described apparatus. Thuscorresponding reference numerals are used in FIGS. 3 and 4 forcorresponding parts in FIGS. 1 and 2, and they are not furtherdescribed. This embodiment provides for more flexibility of operation,in that the deposition rate for each set of blocks may be selected byselecting the respective block speeds. Thus, in a two colour situation,if one wished the volume of one component deposit to be twice the volumeof the other, one could use single colour, similarly sized blocks andfeed one set at twice the speed of the other, whereas in the earlierdescribed embodiment it would be necessary to manufacture blocksincluding the two components in the requisite proportions. Incidentally,it should be noted that the block speed directly determines the volumeof the deposit. However, as the specific gravities of differentlycoloured pigments usually differ it follows that equal speeds of equallysized blocks will rarely produce equal masses of deposited components.As the effect on the eye may depend to some extent on the relativemasses of pigment in the finished coating, the actual block speeds mayhave to be adjusted to suit. Therefore it is important that the sizesand weights of the blocks and the block speeds be recorded in anyinstance, to enable accurate pattern replication to be achieved at alater date.

The effect of varying the respective block speeds and dispositions isillustrated by FIGS. 10 to 13.

FIG. 10 shows a pattern produced when blocks 23(a) are the lighterblocks and the block speeds were selected so that the long termdeposition rate of the lighter blocks 23(a) was approximately 70% ofthat of the darker blocks 23(b).

FIG. 11 shows the pattern produced under the same conditions as for FIG.10 except that the deposition rate of the lighter blocks 23(a) wasapproximately 25% that of the darker blocks 23(b).

FIG. 12 shows the pattern when the lower blocks 23(a) were the darkerand the long term deposition rate of those darker blocks wasapproximately 140% of that of the lighter blocks 23(b). The relativemasses of the respective colours in this case is substantially the sameas it was in the FIG. 10 example, but the effect on the eye is quitedifferent.

FIG. 13 shows the pattern when the lower blocks 23(a) were the darkerand had a long term deposition rate of approximately 45% of that of thelighter blocks 23(b).

It will be noted that in each illustration, a row of three blocks isprovided at each melt deposition site, so that the total target area ineach case approximately spans the width of the strip. Such a span ispreferred as it facilitates satisfactory spreading of the melt depositsinto a continuous coat. It should also be noted, however, that this useof multiple blocks in rows (instead of a single block providing the sameor similar span) provides for another variable in the selection of thefinished pattern, in that the order of deposition of the components fromeach block of FIG. 1 or each aligned pair of blocks of FIG. 3 is notnecessarily the same as for the neighbouring blocks in the row.

What is claimed is:
 1. A method of continuously producing a continuouspaint coat of substantially constant, pre-determined thickness, anddisplaying a plural colour, familial, non-modular pattern, on a surfaceof a moving substrate, comprising the steps of depositing at least twodiscontinuous, randomly patchy, differently coloured, component paintdeposits, at a predetermined, constant, long term deposition rate foreach component deposit in terms of the volume of paint per unit area ofthe surface, within a stationary target area of the surface andthereafter spreading and smoothing the component paint deposits carriedby the substrate from the target area, to form the continuous coathaving a familial, non-modular pattern.
 2. A method of continuouslyproducing a continuous paint coat of substantially constant,pre-determined thickness, and displaying a plural colour, familial,non-modular pattern, on a surface of a moving substrate, comprising thesteps of depositing at least two discontinuous, randomly patchy,differently coloured, component paint deposits, at a predetermined,constant, long term deposition rate for each component deposit in termsof the volume of paint per unit area of the surface, within stationarytarget areas of the surface respectively associated with the componentdeposits and at least partly aligned in the direction of movement of thesubstrate, and thereafter spreading and smoothing the component paintdeposits carried by the substrate from the target areas, to form thecontinuous coat having a familial, non-modular pattern.
 3. A methodaccording to claim 2 wherein the component deposit in each target areais of a single colour which is different from the single colour of thecomponent deposit in at least one other target area.
 4. A method ofpainting at least a part of a side face of a moving substrate striputilising a paint composition having a glass transition temperature, ofthe kind comprising the steps of pre-heating the strip to a pre-heattemperature above said glass transition temperature, moving thepre-heated strip at a pre-determined strip speed, driving a solid blockof the paint composition along an axis of the block at a pre-determinedblock speed towards said side face to cause a liquid deposit of saidpaint composition to be melted from the block and carried away from theblock on said face, spreading and smoothing the carried away liquiddeposit, and thereafter allowing or causing the smoothed liquid depositto solidify, characterised in that said block comprises at least twodifferently coloured components, in that the pre-heat temperature isabove the glass transition temperatures of all of the components, inthat the block speed is so low as to ensure that the carried awaydeposit is a discontinuous patchy deposit, and in that the spreading andsmoothing converts the discontinuous patchy deposit into a continuouscoat displaying a familial, non-modular colour pattern.
 5. A methodaccording to claim 4 wherein the respective volumes of said componentsof the block are in pre-determined proportions.
 6. A method according toclaim 5 wherein the said components display a marbled pattern within theblock.
 7. A method according to claim 5 wherein each said component ofthe block is of constant cross-section on a section plane normal to thedirection of movement of the block.
 8. A method of painting at least apart of a side face of a moving substrate strip utilising a paintcomposition having a glass transition temperature, of the kindcomprising the steps of pre-heating the strip to a pre-heat temperatureabove said glass transition temperature, moving the pre-heated strip ata pre-determined strip speed, driving a solid block of the paintcomposition along an axis of the block at a pre-determined block speedtowards said side face to cause a liquid deposit of said paintcomposition to be melted from the block and carried away from the blockon said face, spreading and smoothing the carried away liquid deposit,and thereafter allowing or causing the smoothed liquid deposit tosolidify, characterised in that at least one further said block at leastpartly differing in colour from the first mentioned block and in atleast partial alignment with the first mentioned block in the directionof strip travel is likewise driven towards the side face at a secondpre-determined block speed, in that each block speed is so low as toensure that each of the carried away deposits is a discontinuous patchydeposit, and in that the spreading and smoothing converts all of thecarried away deposits into a continuous coat displaying a familial,non-modular colour pattern.
 9. A method according to claim 8 whereinsaid first and second predetermined block speeds are equal.
 10. A methodaccording to claim 8 wherein each said block is of a single colour. 11.A method according to claim 8 wherein at least one of said blockscomprises at least two differently coloured components, and wherein therespective volumes of said components of said at least one block are inpre-determined proportions.
 12. A method according to claim 11 whereineach said component of said at least one block is of constantcross-section on a section plane normal to the direction of movement ofthe block.